Atomic Theory

Thales

600 BCE

Thales of Miletus, the earliest of the Ionian philosophers, initiated the revolutionary notion that to understand the world one needed to know its nature ( 'physis', hence the modern 'physics' ) and that there was an explanation for all phenomena in natural terms.
That was a giant step from the assumptions of the old world that supernatural forces determined almost everything.

The Greek philosopher, Democritus

465 BCE

His atomic theory is:
1.All matter consists of invisible particles called atoms.
2. Atoms are indestructible.
3. Atoms are solid but invisible.
4. Atoms are homogenous.
5. Atoms differ in size, shape, mass, position, and arrangement.
- Solids are made of small, pointy atoms.
- Liquids are made of large, round atoms.
- Oils are made of very fine, small atoms that can easily slip past each other.

Aristotle

322 BCE

Aristotle did not believe in the atomic theory and he taught so otherwise. He thought that all materials on Earth were not made of atoms, but of the four elements, Earth, Fire, Water, and Air. He believed all substances were made of small amounts of these four elements of matter. Most people followed Aristotle’s idea, causing Democritus’ idea to be over looked for about 2,000 years. Finally Aristotle's theory has been proven incorrect and that everything on earth is made of matter.

Issac Newton

1660

Newton studied gases, and the possibility of atoms existing, and like Boyle, his work was impeded by the church. He proposed a mechanical universe where small solid masses were in motion. In short, he believed that there were little tiny pieces of mass that were 'swimming' everywhere.
He began to understand that atoms or particles move and are not stationary.

John Dalton

1803

John Dalton's commitment to the atomic theory:
1. Matter is made up of atoms that are indivisible and indestructible.

1. All atoms of an element are identical.
2. Atoms of different elements have different weights and different chemical properties.
3. Atoms of different elements combine in simple whole numbers to form compounds.
4. Atoms cannot be created or destroyed. When a compound decomposes, the atoms are recovered unchanged.

Michael Faraday

1832

Through Michael Faraday's research of the magnetic field around a conductor carrying the direct current, Faraday made the basis of the concept of the electromagnetic field in physics. He established that magnetism could affect rays of light and that there was an underlying relationship between the two phenomena.

J. Plucker

1859

In 1847 he began research on the behaviour of crystals in a magnetic field, establishing results central to a deeper knowledge of magnetic phenomena. Plucker built one of the first gas discharge tubes ("cathode ray tube").

Dmitri Mendeleev

1869

Arranged elements into 7 groups with similar properties. He discovered that the properties of elements "were periodic functions of the their atomic weights". This became known as the Periodic Law.

James Clerk Maxwell

1873

James Clerk Maxwell's contribution to the atomic concept had to do with his theory of electromagnetism. His mathematical laws of electrodynamics, formulated between 1864 and 1873, describe the phenomenon of electromagnetic radiation and build directly upon the earlier speculations of Michael Faraday. He also proposed electric and magnetic fields filled the void.

Sir William Crookes

1879

Sir William Crookes discovered cathode rays had the following properties: travel in straight lines from the cathode; cause glass to fluoresce; impart a negative charge to objects they strike; are deflected by electric fields and magnets to suggest a negative charge; cause pinwheels in their path to spin indicating they have mass.

E. Goldstein

1886

E. Goldstein used a CRT to study "canal rays" which had electrical and magnetic properties opposite of an electron.

Wilhelm Roentgen

1895

Using a CRT he observed that nearby chemicals glowed. Further experiments found very penetrating rays coming from the CRT that were not deflected by a magnetic field. He named them "X-rays".

Henri Becquerel

1896

While studying the effect of x-rays on photographic film, he discovered some chemicals spontaneously decompose and give off very pentrating rays.

J.J. Thomson

1897

Used a CRT to experimentally determine the charge to mass ratio (e/m) of an electron =1.759 x 10 8 coulombs/gram.
J.J. Thomson Studied "canal rays" and found they were associated with the proton H +.

Rutherford

1898

Studied radiations emitted from uranium and thorium and named them alpha and beta.

Marie Sklodowska Curie

1898

Studied uranium and thorium and called their spontaneous decay process "radioactivity". She and her husband Pierre also discovered the radioactive elements polonium and radium.

Richard Abegg

1904

Discovered that inert gases had a stable electron configuration which lead to their chemical inactivity.

Hantaro nagaoka

1904

In 1904, Nagaoka proposed an alternative planetary model of the atom in which a positively charged center is surrounded by a number of revolving electrons, in the manner of Saturn and its rings. Nagaoka's model made two predictions: a very massive atomic center (in analogy to a very massive planet)

H.G.J. Moseley

1914

Using x-ray tubes, determined the charges on the nuclei of most atoms. He wrote"The atomic number of an element is equal to the number of protons in the nucleus". This work was used to reorganize the periodic table based upon atomic number instead of atomic mass.

Niels Bohr

1922

Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of sucessive orbital shells of electrons.

Francis William

1922

Francis William, who won the Nobel Prize for Chemistry in 1922 for his discovery of a large number of isotopes (atoms of the same element that differ in mass), using a mass spectrometer, and for formulating the “whole number rule” that isotopes have masses that are integer values of the mass of the hydrogen atom.

Louis de Broflie

1923

Discovered that electrons had a dual nature-similar to both particles and waves. Particle/wave duality. Supported Einstein.

G.J. Stoney

1984

G.J. Stoney proposed that electricity was made of discrete negative particles he called electrons ". (Link to info on electrons)

Max Planck

1990

used the idea of quanta (discrete units of energy) to explain hot glowing matter.

Fredrick Soddy

1990

Observed spontaneous disintegration of radioactive elements into variants he called "isotopes" or totally new elements, discovered "half-life", made initial calculations on energy released during decay.